Technical Field
The present invention relates to a method and an apparatus for additive manufacturing.
Description of Related Art
Freeform fabrication or additive manufacturing is a method for forming three-dimensional articles through successive fusion of chosen parts of powder layers applied to a worktable.
An additive manufacturing apparatus may comprise a work table on which the three-dimensional article is to be formed, a powder dispenser, arranged to lay down a thin layer of powder on the work table for the formation of a powder bed, an energy beam for delivering energy to the powder whereby fusion of the powder takes place, elements for control of the energy given off by the energy beam over the powder bed for the formation of a cross section of the three-dimensional article through fusion of parts of the powder bed, and a controlling computer, in which information is stored concerning consecutive cross sections of the three-dimensional article. A three-dimensional article is formed through consecutive fusions of consecutively formed cross sections of powder layers, successively laid down by the powder dispenser.
In additive manufacturing it is important to control the powder distribution. It is desirable to distribute a predefined amount of powder over a predetermined area. When fusing the powder at selected locations according to a 3-dimensional model with an electron beam the powder may start to “smoke”, i.e., the electron beam may charge the powder particles, which in turn may start to repel each other and lift from the powder bed. Such “smoke” of powder is highly undesirable because, if it happens, the additive manufacturing process is most likely to be stopped. In order to prohibit powder “smoke” there are different methods used such as preheating of the powder layer to be fused and/or reduced power of the fusing beam. These methods may increase the build time which may be a problem.